Swapping 700x25C for 700x23C tyres

[TomUK]

Thanks 'hgf'.
Must say that the hooks shown on the diagram (which I also saw on Sheldon Brown's site) look more pronounced than the slight ridge on my Raleigh rims - but hey! - the tyres stayed on so everthing's fine!

 

[ASC1951]

counterintuitively studies show wider tyres have a lower rolling resistance than thinner tyres.

Only up to a point. It depends on tyre pressure, road surface and temperature. I thought the studies showed that in most conditions, and particularly on warm tarmac, correctly inflated 23s were faster than both 25s and 18s. 23s are certainly most people's choice for general riding.